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From: wbe@BBN-VAX.ARPA
Newsgroups: net.micro.amiga
Subject: MMUs versus memory protection
Message-ID: <461@caip.RUTGERS.EDU>
Date: Sun, 17-Nov-85 09:32:24 EST
Article-I.D.: caip.461
Posted: Sun Nov 17 09:32:24 1985
Date-Received: Mon, 18-Nov-85 07:48:03 EST
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Organization: Rutgers Univ., New Brunswick, N.J.
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From: "Winston B. Edmond" <wbe@BBN-VAX.ARPA>

   There seems to be this persistent belief that memory management is
needed to get memory protection.  It's not true.

   Memory management allows one to have segmentation and/or paging, and
has some kind of memory mapping arrangement.  Manufacturers of
inexpensive, high performance systems look at these and say "Address
translation will slow down the system and cost more money.  Let's not
do it."  They may even be right, in the sense that their intended
market may not need it.

   Memory protection can be as simple as base-bounds registers, which
specify the lowest and highest allowed addresses.  It does not require
address translation, and does not slow down the machine.  What it does
do is detect out-of-bounds references and trap to the operating system.

   Memory protection is enough to make debugging in multi-processing
systems fairly safe.  Unfortunately, in my opinion, most manufacturers
seem to decide that it's either full memory management or nothing.

~~flame warning~~
   The view that consumers won't care because they buy working products
rather than develop them, and that there aren't enough developers to
make the additional cost worthwhile, overlooks something.  A system
that is easier for developers will make software products appear sooner.
This helps sell more computers.  If debugging is easier, the products
will be more thoroughly tested and reliable, which makes the developers
look good, which makes them happier they chose to write software for
that machine.
__end flame__

   Are there any plans for an Amiga II that supports memory protection
or memory management?
 -WBE